The present invention relates to a photoresist laminate and a method of patterning by using the same. More particularly, the invention relates to a photoresist laminate capable of giving a patterned resist layer of high pattern resolution having an excellently orthogonal cross sectional profile as well as to a method for the formation of a patterned resist layer by using the photoresist laminate.
It is a remarkable trend in recent years in the fields of manufacturing semiconductor devices along with the rapid increase in the degree of integration of the devices that the photolithographic patterning of a resist layer on a substrate is performed by using actinic rays having a shorter and shorter wavelength than in the prior art. Thus, the actinic rays as a major current in recent years used for the purpose include i-line light of 365 nm wavelength, deep ultraviolet light, excimer laser beams and the like. A problem accompanying the use of such short-wavelength actinic rays is that reflection of the actinic rays on the substrate surface bearing the photoresist layer is increased while the reflecting light causes a phenomenon of local distortion or notching of the patterned resist layer or a decrease of the dimensional accuracy of the pattern.
As a method for overcoming the troubles due to reflection of light on the substrate surface, a proposal is made to provide an anti-reflection film as an undercoating of the photoresist layer on the substrate surface to form a photoresist laminate. The photoresist composition currently under use in many cases with such an anti-reflection undercoating is a photoresist composition of the so-called chemical-sensitization type in view of the high photosensitivity and high pattern resolution obtained therewith. Chemical-sensitization photoresist compositions, which can be classified into positive-working and negative-working compositions, contain a radiation-sensitive acid-generating compound and a resinous film-forming ingredient which causes a decrease or increase, respectively, of the solubility in an aqueous alkaline solution by the catalytic activity of the acid generated from the acid-generating agent in the areas of the photoresist layer pattern-wise exposed to actinic rays.
The above mentioned resinous film-forming ingredient in the positive-working chemical-sensitization photoresist composition is usually an alkali-soluble resin such as a polyhydroxystyrene resin or a copolymeric resin of a hydroxy-styrene and another styrene monomer in combination with an alkali-solubility reducing agent which causes an increase in the alkali solubility by reacting with an acid or an alkali-soluble resin such as a polyhydroxystyrene resin substituted for a part of the hydroxyl groups by alkali-solubility reducing groups.
The resinous film-forming ingredient in the negative-working chemical-sensitization photoresist composition, on the other hand, is a combination of an acid-crosslinkable compound and an alkali-soluble resin such as a polyhydroxystyrene resin or a copolymeric resin of a hydroxystyrene and another styrene monomer, optionally, substituted for a part of the hydroxyl groups by alkali-solubility reducing groups to be rendered alkali-insoluble.
When the above described chemical-sensitization photoresist composition or, in particular, the negative-working one is used for patterning as a photoresist laminate with an anti-reflection undercoating, it is sometimes the case that necking or constriction of the patterned photoresist layer at the interface with the anti-reflection undercoating layer sometimes occurs to affect the orthogonality of the cross sectional profile of the patterned resist layer. When the anti-reflection undercoating layer is to be removed by dry etching with such a poorly patterned resist layer as an etching mask, the etching treatment cannot be performed with high dimensional accuracy not to accomplish patterning with high pattern resolution.